1. Field of the Invention
This invention relates to a mechanism having an elongated member such as a shaft, plunger or rod that has been formed to present a stop. The stop prevents relative movement between the member and another component of the mechanism in directions parallel to the longitudinal axis of the member.
2. Description of the Related Art
Many types of mechanisms in common use include a stop for limiting relative movement between one member and another member of the mechanism. In some instances, the stop is provided to prevent disengagement and separation of the members from each other. In other instances, the stop is provided to limit relative movement of the two members to a range that is deemed desirable for satisfactory performance of the mechanism.
For example, some rotating mechanisms have a first member that is a wheel, drum, roller or pulley and have a second member that extends through the first member. The second member may be a shaft, axle or rod or other type of component. The two members are movable relative to each other in arcs that extend about the longitudinal axis of the second member. For example, the first member may be stationary while the second member revolves, or the second member may be stationary while the first member revolves. In some instances, both of the members are freely rotatable in directions about the longitudinal axis of the second member.
In the rotating mechanism described above, one or more stops are often provided for limiting relative movement of the two members in directions parallel to the longitudinal axis of the second member. For example, a pair of cylindrical sleeves might be fixed to a shaft on opposite sides of a wheel to keep the wheel in place and prevent the wheel from disengaging the shaft. In those instances, the sleeves permit free relative pivotal movement of the wheel and shaft in directions about the longitudinal axis of the shaft, but limit the extent of sliding movement of the wheel in directions parallel to the longitudinal axis of the shaft.
Other examples of mechanisms with stops include various types of sliding mechanisms. A sliding mechanism may include, for instance, a first member having a channel and a second member that is partially received in the channel. The members are movable relative to each other in directions parallel to the longitudinal axis of the second member. For instance, the second member may slide along the channel while the first member is stationary, or the first member may slide along the length of the second member while the second member is stationary. In other instances, both of the members may be freely movable.
One well-known example of a sliding mechanism is a telescoping-type of mechanism where the channel of the first member has a shape that surrounds and is complemental to the shape of the second member when considered in reference planes that are perpendicular to the longitudinal axis of the second member. In those mechanisms, the second member may be provided with one or more stops to limit relative sliding movement. For instance, the second member may have a stop that is intended to prevent the second member from moving out of the channel and disengaging the first member. In other instances, the second member may have a stop that limits sliding movement for other reasons that are deemed necessary or practical for satisfactory operation of the mechanism.
An example of a telescoping mechanism having a stop is described in U.S. Pat. No. 5,964,588, assigned to the assignee of the present invention. The mechanism described in that patent is an intra-oral device for applying a force to the upper and lower dental arches of a patient undergoing orthodontic treatment, and includes a spring that tends to move the relative positions of the upper and lower dental arches when the patient""s jaws are closed.
The force module described in U.S. Pat. No. 5,964,588 includes a collar that is mounted on one member. The collar functions as a stop to limit sliding movement of two members relative to each other. The position of the collar on the member can be selected by the orthodontic practitioner so that the spring provides the desired amount of biasing force when the patient""s jaws are closed. In certain embodiments of the force module described in that patent, the collar is in the shape of a cylindrical sleeve that is fixed to the member by, for example, a welding, brazing or crimping operation.
Over the years, there has been a continuing interest in reducing manufacturing costs, including the costs of making various types of moving mechanisms. As a result, efforts have been directed to simplify the manufacture of stops that are present in movable mechanisms. In this regard, the provision of a stop can add considerable expense to the cost of manufacturing a mechanism, even though the function of the stop may be deemed relatively simple.
For example, the manufacture of the orthodontic force module described in the aforementioned U.S. Pat. No. 5,964,588 may include several steps related to the stop or collar. For instance, the method may include the step of cutting a section of tubular cylindrical stock to a desired length to make a stop or collar. Next, both the collar and the member receiving the collar are cleaned as needed. The collar is then positioned at an appropriate place along the length of the member and is tack-welded in place to hold its position. The collar is then brazed to the member in an oven to provide a strong, secure connection between the collar and the member. Finally, the collar and member are cleaned and assembled to remaining components of the force module.
By contrast, some movable mechanisms have stops that are integral with one of the members. As can be appreciated, such construction avoids the need to manufacture and assemble two separate components. Optionally, the manufacture of integral stops is carried out in automated fashion, so that the stop is automatically placed at its desired location along the length of the member in each instance.
One common example of a movable mechanism with an integral stop is a toy vehicle having a wheel that is mounted on a cylindrical shaft. The ends of the shaft are deformed during manufacture to a flattened configuration. The increased width of the flattened ends in directions perpendicular to the longitudinal axis of the shaft is greater than the diameter of the hole in the wheel. Consequently, the flattened ends of the shaft prevent the wheel from disengaging the shaft. However, the wheel is located over the cylindrical portion of the shaft and can turn as needed about the longitudinal axis of the shaft.
The flattened, integral stop as described above is satisfactory for use in many types of mechanisms, especially in mechanisms where substantial forces are not expected to be encountered. However, in other instances, the presence of substantial forces may cause the mechanism to fail. Such a failure is particularly problematic in instances where it is not desirable or practical to simply increase the size of the members to increase their strength.
The telescoping intra-oral force module described in U.S. Pat. No. 5,964,588 may encounter significant forces in use. For example, significant forces may be imposed on the force module during mastication, especially when the patient is chewing a relatively hard food object. If the flattened stop described above is substituted for the collar stop, the resulting assembly may bend or break during use and prompt the patient to return to the orthodontist""s office for repair or replacement. As can be appreciated, such a failure represents a nuisance to both the practitioner and the patient in terms of time and expense.
Moreover, it would not be deemed desirable to simply increase the overall size of the orthodontic force module members in the hypothetical example described above in order to avoid such failures. The space in the oral cavity is somewhat limited and is occupied by other components of the orthodontic system as well, including brackets and archwires. An increase in size of the force module may cause the force module to impinge on the patient""s soft tissue adjacent the cheeks and lips, resulting in discomfort.
From the foregoing, it can be appreciated that there is a need in the art for an improved stop for a movable mechanism that does not unduly increase the cost or size of the mechanism or increase the likelihood that the mechanism will fail during use.
The present invention is directed to a movable mechanism having stop that is integrally formed in one member of the mechanism. The stop is made by forming at least three impressions in the member that are spaced apart from each other when considered in reference planes perpendicular to the longitudinal axis of the member. The impressions so formed result in three or more distinct lobes that extend outwardly from the longitudinal axis a distance sufficient to function together as a stop.
Surprisingly, it has been found that the resulting stiffness of the member is increased about multiple reference axes in sections of the member where the lobes are present in comparison to remaining sections of the member that lack the lobes. As such, the resulting mechanism is less likely to fail in use, regardless of the direction of the imposed force.
The present invention is a substantial advantage over mechanisms having stops that are made by flattening opposite sides of a cylindrical member to present two oppositely-extending lobes. In the latter instance, the stiffness of the member is increased in the direction of extension of the lobes but is decreased in perpendicular directions. As a result, that stop may bend or fracture if substantial forces are encountered in the latter directions.
In more detail, the present invention in one aspect is directed to a mechanism that comprises a first member having a channel and a second member having a generally cylindrical portion at least partially received in the channel. The cylindrical portion has a longitudinal axis. The first member and the second member are movable relative to each other in directions along the longitudinal axis. The second member also has a stop portion for limiting relative movement between the first member and the second member in directions along the longitudinal axis. The stop portion is made of a formable material and the material is formed to present at least three lobes that extend outwardly in different respective directions from the longitudinal axis.
Another aspect of the invention is directed to a sliding mechanism. The mechanism includes a receiving member having a channel and a plunger having a generally cylindrical portion at least partially received in the channel. The cylindrical portion has a longitudinal axis. The plunger and the receiving member are slidably movable relative to each other in directions along the length of the longitudinal axis. The plunger also has a stop portion for limiting relative sliding movement between the plunger and the receiving member. The stop portion is made of a formable material and the material is formed to present at least three lobes that extend outwardly in different respective directions from the longitudinal axis.
The present invention is also directed to a rotating mechanism. In this aspect, the mechanism includes a first member having a channel and a second member having a generally cylindrical portion at least partially received in the channel. The cylindrical portion has a longitudinal axis. The first member and the second member are rotatable relative to each other in directions about the longitudinal axis. The second member also has a stop portion for limiting relative sliding movement between the first member and the second member in directions along the longitudinal axis. The stop portion is made of a formable material and the material is formed to present at least three lobes that extend outwardly in different respective directions from the longitudinal axis.
An additional aspect of the present invention is related to an intra-oral force module for moving the relative positions of the upper and lower dental arches. The force module comprises a first member having a channel and a second member having a generally cylindrical portion at least partially received in the channel. The cylindrical portion has a longitudinal axis. The first member and the second member are slidable relative to each other in directions along the length of the longitudinal axis. The second member also includes a stop portion for limiting relative sliding movement of the first member and the second member. The stop portion is made of a formable material and the material is formed to present at least three lobes that extend outwardly in different respective directions from the longitudinal axis.
Other aspects, features and advantages of the present invention are described in the paragraphs that follow and are illustrated in the accompanying drawings.